1. Field of the Invention
The present invention relates generally to a device used for threading a web of material through a rotary printing press.
2. Related Art
Rotary printing presses typically require that a paper web be threaded through the press each time a new paper roll is to be used. Presses typically require long lengths of paper, and the paper path is generally circuitous. Thus, threading paper through such a press can be a tricky and cumbersome procedure.
Devices, commonly referred to as xe2x80x9csnakes,xe2x80x9d have been developed for threading the web around guide rollers and turning bars in the press. In use, the end of the web is connected to the snake, and the snake leads the web through the printing press. The snakes are made to run along tracks, shaped and curved to match the desired web path. When guided along such a track, a snake must be flexible enough to achieve the tight turns and bends required by the web path.
Typically, snakes have been made from chains, ropes or thin pieces of compliant materials, pushed and pulled along the web path by rollers or other powered devices. One common type of snake is made of a chain, which is advanced along a track by sprockets. However, use of chains is difficult, dirty, and the chain links are apt to break. Further, a chain can come off a sprocket or out of the track, requiring maintenance, during which time that portion of the press is not operational.
Another known snake includes riveted guides attached directly through the snake body. The snake relies on the guides to maintain the snake in the track. With this type of snake, the riveted guides run inside the track, directing the snake through the desired web path. However, a snake with riveted guides is unreliable, as the riveted guides may break in the track or may become disconnected from the snake, jamming the track and requiring instant maintenance during which time that portion of the press is not operational. Further, maintenance of the snake itself is difficult and cumbersome, as replacement rivets must be manually attached to the snake.
Another snake device, shown in U.S. Pat. No. 5,996,873, runs externally on a track and is comprised of a number of individual segments, joined using bosses retained by holes. The segments rotate along the track path so that the snake can follow any helical path which may be required to lead the web through the angle bars, around the guide rollers or through other parts of the printing press. A snake comprised of individual segments requires maintenance for each segment. The inter-working pieces are subject to binding and other problems which may result in difficulties with threading the web and can lead to maintenance and repairs during which time that portion of the press is not operational.
Another snake device, shown in U.S. Pat. No. 5,400,940, is a single element snake used for threading a web through a printing press. The snake is a thin member having either transverse grooves or through holes for meshing with sprockets to propel the snake through the system. Such a snake is required to be completely enclosed within the track system, except at the sprocket access points, to avoid the problem of the snake inadvertently separating from the track during use. As such, the snake is virtually inaccessible and any problem associated with the snake while threading a web would result in the press being out of operation. Also, if the sprockets do not mesh properly with the grooves or though holes, the press must be shut down and the snake realigned.
Therefore, what is needed is a snake for threading a web through a printing press that is reliable, has minimal parts that will not uncouple and lodge in the track or press, and that is easily accessible as maintenance is required.
The present invention smoothly and efficiently threads a web through a printing press, while avoiding costly maintenance and press downtime. Specifically, the invention is directed to a snake apparatus for threading a web through a printing press. The snake is comprised of a body portion and at least one ridge integrally formed on at least one surface of the body portion. The ridge extends the length of the body and is configured to engage and guide the snake along a track through the printing press. The snake may have a ridge on one side, a ridge on each side, or may have more than one ridge on each side. The ridge includes intermittently spaced gaps, which provide flexibility to the body portion. The gaps are notches in the ridges, which are aligned with corresponding gaps on any opposite ridges so that the snake can easily flex and bend without compressing or placing in tension any of the ridges. The snake further includes a means for attaching the web to the snake. The means could be a brass grommet to which an end of the web is tied.
The present invention also includes a method for threading a web through a printing press using the snake of the present invention. In particular, the snake is used by attaching one end of the web to the snake, and inserting the front end of the snake into a track that extends through the press in the desired path. The ridges on the snake are fed into a ridge guide, formed as a part of the track. The snake is propelled along the track by powered driving members which have wheels to frictionally engage the snake. The web, attached to the snake, likewise advances along the desired track through the printing press.